As Guy said, this is usually if your PC is having problems handling the framerate. Try the suggestions I gave earlier for playing in windowed mode and at a lower resolution. If that still doesn't work, consider uploading the savegame and see if someone can play past it for you.

What are your PC specs? ›››

(Moved to TW2 forum)

You don't need the trap. If you've got to the point where you're sitting on his arm, you're almost there.

Once you're sitting on one of his arms, there should be a QTE symbol come up on the screen asking you to left-click. You need to keep on clicking until the bar is filled, then you'll land on the ground again. After that, you run to the left and climb up onto the fallen bridge, and run up the bridge until it switched to a cutscene. Then it'll all be over.

I suggest you look at a youtube video to see the details on where the bridge is and how to climb it. ›››